The present invention relates to a sulphur source for fungi and a method for using the same to promote the growth of fungi in the rumen of a ruminant animal. More particularly, the present invention relates to a method for promoting the growth of anaerobic fungi in the rumen of animals fed on low sulphur content diets.
The rumen or forestomach is an organ found in the digestive tract of certain herbivorous mammals. The rumen is located prior to the gastric stomach and is the site where digestion and fermentation of plant material occurs through the activity of microbial populations.
Anaerobic fungi, bacteria and protozoa represent the three major groups of microorganisms in the rumen. The anaerobic fungi make a vital contribution to the digestion of plant fibre and in particular, plant fibre in poor or low quality feed. Poor quality feed often lacks one or more dietary components which may affect the microbial populations in the rumen. In particular, when ruminant animals consume a low sulphur content diet the population of anaerobic fungi in the rumen may be significantly reduced. A reduction in the fungi population can hamper the digestion of feed which in turn may reduce feed intake and cause the animal to have a reduced productivity.
Fungi in the rumen require sulphur in reduced form to meet their growth requirements. When sulphur is administered to the rumen as dietary sulphur it is mostly degraded to sulphide by bacteria and used by fungi and other microorganisms in the rumen. Any remaining sulphide is transported across the rumen wall and out of the rumen. Thus, sulphide does not persist in the rumen.
The effect of low sulphur diets on the population of anaerobic fungi in the rumen was observed in 1983. Since that time a number of sulphur sources have been used to supplement the diet of ruminant animals fed on low sulphur diets. For example, sulphur in the form of sodium sulphate has been added directly to feed sources such as pastures with low sulphur contents, and the sulphur containing amino acid, methionine, has been administered to animals as a feed supplement.
Whilst the prior art sulphur sources outlined above have been found to promote the growth of ruminant fungi and increase the intake of feed by ruminant animals, they are degraded to sulphide by bacteria in the rumen at a rate that is greater than the rate at which the fungi in the rumen use the resulting sulphide. Thus, a large amount of the sulphide produced is not used by the fungi.
The rate of degradation of the prior art sulphur sources, and to a certain extent their mode of administration, means that relatively large amounts need to be administered to deliver an effective dose of sulphur to fungi in the rumen of a ruminant animal. The large amounts of the sulphur sources used cause the methods to be relatively expensive and inefficient.
The present invention seeks to overcome or at least partially alleviate the problems identified above.
The present invention provides a method for promoting the growth of at least one anaerobic fungus in the rumen of a ruminant animal, the method comprising the step of administering to the rumen an effective amount of a degradation resistant sulphur source.
Throughout this specification, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, or variations such as xe2x80x9ccomprisesxe2x80x9d or xe2x80x9ccomprisingxe2x80x9d will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers including method steps.
Further, throughout the following description reference will be made to xe2x80x9cruminant animalsxe2x80x9d which will be understood to include all ruminant and ruminant-like animals, being members of the Order Artiodactyl and having a pre-gastric fermentation in a rumen (for ruminant animals), or a similar part of the digestive tract such as the paunch (for ruminant-like animals).
For the purposes of the present invention the term xe2x80x9cdegradation resistantxe2x80x9d is to be interpreted in terms of the microbial population in the rumen. Thus, a xe2x80x9cdegradation resistant sulphur sourcexe2x80x9d is a sulphur source that is degraded by microorganisms in the rumen, such as bacteria, to sulphide at a slower rate than the prior art sulphur sources so that it remains available to fungi for a longer period of time.
The degradation resistant sulphur source may be varied. Preferably, the degradation resistant sulphur source is 3-mercaptopropanoic acid (MPA) or a functional equivalent thereof. Functional equivalents for the purposes of the present invention include; the salts of MPA with monovalent and divalent cations such as sodium, potassium, calcium, copper, zinc and magnesium salts; the esters of MPA incorporating alkyl groups such as methyl, ethyl and butyl groups and; the dimer form of MPA, in which two MPA monomers are linked by a disulphide bond.
The sulphur source may be administered in any of a number of ways apparent to one skilled in the art. Preferably, the sulphur source is administered intra-ruminally or orally as a feed supplement. When the sulphur source is administered intra-ruminally, it is preferably administered using a controlled release device such as the device described in Australian patent 555998.
The degradation resistant nature of the sulphur source of the present invention allows it to be administered in smaller doses and less often relative to other sulphur sources. In this respect, the sulphur source of the present invention is degraded by microorganisms such as bacteria in the rumen at a slower rate than the prior art sulphur sources and thus continues to be available in the rumen for longer periods of time.
The effective dose may be varied and may be at least partially dependent on the type of ruminant animal receiving the dose and the amount of sulphur the animal is extracting from its regular intake of feed. In this respect, it is expected that the larger the animal receiving the dose, the larger the dose of the sulphur source required to constitute an effective amount will be. Similarly, the higher the sulphur content of a given feed, the smaller the dose of the sulphur source required to constitute an effective amount will be. It will be appreciated that the optimum dose for a particular animal could be readily determined by one skilled in the relevant art.
Preferably, the effective dose of MPA is such that the concentration of MPA in the rumen is approximately 0.2 mM to 8 mM. Even more preferably, the effective dose of MPA is such that the concentration of MPA in the rumen is approximately 0.2 to 4 mM. In one particularly preferred form, the effective dose of MPA is such that the concentration of MPA in the rumen is approximately 0.75 to 1.5 mM.
The effective dose required to produce the MPA concentrations outlined above varies. Preferably, and when the ruminant animal is a sheep, the effective dose is approximately 25-200 mg Sulphur/day or more preferably, approximately 95-190 mg Sulphur/day. For example, when the sulphur source is MPA and the ruminant animal is a sheep fed on a low sulphur diet (approximately 0.06% sulphur), the effective dose of MPA is preferably approximately 190 mg Sulphur/day.
The method of the invention makes it possible for animals to have an improved productivity. In this respect, and as will be illustrated in the examples below, animals to which the method is applied show improved voluntary feed intake, dry matter digestibility and dry matter digested. The improvement in these characteristics correlates to improved productivity compared to those same animals when not subjected to the method of the invention.
The present invention also provides a veterinary preparation comprising a degradation resistant sulphur source and a suitable carrier.